1. Field of the Invention
The present invention is directed to a transmission with epicyclic trains, particularly for automobiles, buses and industrial vehicles.
2. Description of the Prior Art
There exist mechanisms which, to answer a special need, are realized by means of combining a plurality partial mechanisms such that each of the latter has its own place in a housing and constitutes a removable subassembly. Such a basic mechanism generally has a minimum number of speeds forward and in reverse and as such, suffices, in order to obtain a higher number of speeds, to add one or more of the above-noted necessary partial mechanisms.
This arrangement, while being very flexible, demands the provision for partial mechanisms having complete autonomy from a kinematic point of view and entails, on the whole, a very complicated fabrication with a larger number of elements such as planetary trains, shafts, clutches and brakes than would be utilized in a compact assembly.
To obtain a large number of speeds, it is also possible to dispose such partial mechanisms in series so that the total number of speed ratios is obtained by multiplication of the numbers of speed ratios of each of the partial mechanisms. Evenso, this arrangement, also called a staged mechanism, poses very difficult problems with respect to speed shifting in automatic assemblies.
Furthermore, arrangements with epicyclic trains are also known which allow several speeds forward and several in reverse. These arrangements consist of a compact assembly designed to give the maximum number of speed ratios anticipated and allow smaller numbers of speed ratios by the elimination of clutches, brakes or kinematic elements such as annuli, sun wheels or planet wheels. However, these arrangements, for example in the case of an assembly with six forward speeds and one in reverse, entail a necessarily complicated assembly because of the positioning of the various clutches, different brakes and complex couplings between the various elements of the epicyclic trains.
The essential object of the present invention is the realization of a transmission gear box with epicyclic trains permitting six forward speed ratios and one in reverse, utilizing minimumal mechanical elements such as annuli, planet wheels, sun wheels, clutches and brakes, to name the main elements only.
The transmission box of the present invention is designed so as to obtain easy shifting under load, which results from the fact that shifting from one speed ratio to a ratio directly above or under the speed ratio is effected by a transferring action from a single friction clutch or brake element to another single friction clutch or brake element. The kinematic chain selected permits passing easily from a box with six forward speed ratios to one with five ratios by the elimination of one annulus and one brake characteristic of conventional assemblies.
Similarly, it is possible to obtain a box with four forward speed ratios by the elimination of an annulus, a brake and a clutch in the six-speed box, and one with three forward speed ratios by eliminating an annulus, two brakes and a clutch in the six-speed box.